I've recently inherited a brand which uses Avenir Next as its primary font. Looking through previous documents I have noticed the height of certain characters seem to be off, with the u being the most noticable.
Avenir is a professional typeface family used by many, so its very likely that your copy may have been corrupted in some way. If the copy has been legally purchased this will not happen. You should check with whoever paid for this and make sure you have the right files.
Adobe apps often use custom font rendering algorithms intended to work very fast to cope with complex documents. Unfortunately, they aren't always completely accurate. If this is the issue, a fix is to select View ▸ Display Performance ▸ High Quality Display. Although this will slow your computer down a bit, on modern computers for simple documents it's actually not much of an issue.
Use font-size unit pt instead of px and you'll get a more consistent and crisp result